This proposal focuses on the study and exploitation of the two cloned arginase genes in man, first as a means of elucidating their function, regulation and evolution, and ultimately as a means of devising approaches to replacing the deficient arginase (AI) activity in patients with hyperargininemia and progressive neurological and intellectual deterioration. The cloned AI gene from mouse will be used to create an AI-deficient knockout animal which will be studied to define the pathogenesis of the disorder biochemically and neuropathologically, to study the induction of AII and ultimately as a test subject for molecular studies of gene or "autoenzyme replacement" therapy. cDNAs for non-liver arginase gene(s) (AIIs) will be characterized and be used to isolate the gene or genes encoding them. These reagents will define the cell biology and AII and the regulation of the gene and protein products and the tissue and function specific control of the loci. AI and AII will be used as reagents in gene transfer studies to obtain finer definition of the nature of these regulatory controls. These studies will utilize AI and AII cDNAs under the control of heterologous promotors, as well as constructs of the native gene and regulatory sequences, and reporter genes. Through the molecular manipulation of signal sequences, we will explore the importance of subcellular compartmentalization in the physiologic function of AI and AII and as novel approaches to gene therapy, by redirecting the transferred gene products into or out of the mitochondrion. These studies will define the strategy and tissue specificity for the use of the gene for AI, AII or a combination of the two for gene therapy, or for the recruitment of AII as a means of "autoenzyme replacement". This project exploits a unique model, at a propitious time in an ideal environment, to study the effects of a metabolic disease that causes mental retardation, and its treatment by gene manipulation. Results from these studies should prove relevant to a larger number of disorders of its type.